Lubricating oil composition for automatic transmission

ABSTRACT

A lubricating oil composition provides enhanced anti-wear and anti-seizure properties, even though reduced in viscosity, suitable for use as an automatic transmission oil, particularly as a metal belt continuously variable transmission oil. The lubricating oil composition contains a base oil and the following based on the total mass of the composition: (A) a boron-containing ashless dispersant in an amount of 300 to 1000 ppm by mass on a boron basis, (B) a metallic detergent having a total base number of at least 200 mgKOH/g in an amount of 100 to 1200 ppm by mass on a metal basis, and (C) a friction modifier in an amount of 0.01 to 5 percent by mass. The ratio (Bo/M) of the content of Component (A) on a boron basis (Bo:ppm by mass) to the content of Component (B) on a metal basis (M:ppm by mass) being from 0.5 to 4.

TECHNICAL FIELD

The present invention relates to lubricating oil compositions for automatic transmissions, particularly to a lubricating oil composition for metal belt type continuously variable transmissions.

BACKGROUND ART

Recent automatic transmissions or continuously variable transmissions have been demanded to be light and small and sought to be improved in power transmission capability in connection with the increased power output of the engines with which the transmissions are used in combination. The reduction in weight and size is intended to improve the fuel efficiency of the vehicles in which the transmissions are mounted.

In particular, in the case of a metal belt type continuously variable transmission, it can be reduced in size if the friction coefficient between the belt and pulleys and thus lubricating oil to be used therein is preferably an oil having properties to keep the metal-to-metal friction coefficient high.

Furthermore, the lubricating oil has also been demanded to reduce the fuel consumption. Specifically, a lubricating oil contributes to improvement in fuel economy by reducing its viscosity, stir resistance or viscous resistance upon idling of a clutch pack, or fluid film lubrication, resulting in a reduction in power loss.

A transmission fluid has been proposed, in which a friction modifier, a metallic detergent, an ashless dispersant, and an anti-wear agent are optimally added so as to retain the friction characteristics of a lock-up clutch in a good condition and provide long-lasting initial anti-shudder properties (see Patent Literatures 1 to 7 below).

For example, Patent Literature 1 discloses a transmission lubricating oil composition comprising a specific calcium salicylate, an SP-based extreme pressure additive, a specific succinimide and a boron-containing ashless dispersant, each in a specific amount, which composition exhibits excellent properties such as excellent anti-shudder properties and long-lasting fatigue life. Patent Literature 2 discloses a continuously variable transmission lubricating oil composition containing an organic acid metal salt with a specific composition, an anti-wear agent, and a boron-containing succinimide, as essential components, to have both higher metal-to metal friction coefficient and anti-shudder properties for a slip control mechanism. Patent Literature 3 discloses a long-lasting continuously variable transmission lubricating oil composition comprising calcium salicylate, a phosphorous-containing anti-wear agent, a friction modifier, and a dispersant type viscosity index improver, to have both a higher metal-to metal friction coefficient and anti-shudder properties for a slip control mechanism. Patent Literature 4 discloses a lubricating oil composition comprising a dithiocarbamate compound, a condensate of a branched fatty acid having 8 to 30 carbon atoms and amine, and an amine-based antioxidant, to have excellent and long-lasting anti-shudder properties. Patent Literature 5 discloses an automatic transmission fluid composition comprising calcium sulfonate, phosphorous acid esters and further a sarcosine derivative or a reaction product of a carboxylic acid and amine, to have long-lasting anti-shudder properties for a slip lock-up mechanism and long-lasting properties to prevent scratch noise in a belt type continuously variable transmission. Patent Literature 6 discloses an automatic transmission fluid composition comprising a specific alkaline earth metal sulfonate in a specific amount, which composition is excellent in oxidation stability as a fluid used for an automatic transmission with a slip control mechanism and has long-lasting anti-shudder properties. Patent Literature 7 discloses an automatic transmission fluid comprising calcium salicylate, magnesium salicylate, a specific amount of a friction modifier and a specific amount of a boric acid-modified succinimide, with excellent anti-shudder properties and a certain torque capacity.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2003-113391

Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2001-323292

Patent Literature 3: Japanese Patent Application Laid-Open Publication No. 2000-355695

Patent Literature 4: Japanese Patent Application Laid-Open Publication No. 11-50077

Patent Literature 5: Japanese Patent Application Laid-Open Publication No. 10-306292

Patent Literature 6: Japanese Patent Application Laid-Open Publication No. 10-25487

Patent Literature 7: Japanese Patent Application Laid-Open Publication No. 2000-63869

SUMMARY OF INVENTION Technical Problem

However, when the viscosity reduction is facilitated, oil film at lubricating sites becomes thinner and thus wear and seizure likely occur. Therefore, the present invention has an object to provide a lubricating oil composition which keeps the metal-to-metal friction coefficient higher so that while the torque capacity is maintained, the anti-wear and anti-seizure properties are enhanced even though the viscosity is reduced, particularly suitable as a metal belt type continuously variable transmissions fluid.

Solution to Problem

As the results of extensive studies conducted by the inventors of the present invention to achieve the above object, the present invention was accomplished on the basis of the finding that the above object was able to be achieved with a lubricating oil composition containing a specific boron-containing ashless dispersant and a specific metallic detergent each in a specific amount and a specific ratio.

That is, the present invention provides lubricating oil composition for automatic transmissions comprising a base oil, and on the basis of the total mass of the composition, (A) a boron-containing ashless dispersant in an amount of 300 to 1000 ppm by mass on a boron basis, (B) a metallic detergent with a total base number of 200 mgKOH/g or greater in an amount of 100 to 1200 ppm by mass on a metal basis and (C) a friction modifier in an amount of 0.01 to 5 percent by mass, the ratio (Bo/M) of the content of Component (A) on a boron basis (Bo:ppm by mass) to the content of Component (B) on a metal basis (M:ppm by mass) being from 0.5 to 4.

Advantageous Effect of Invention

The lubricating oil composition of the present invention can keep the metal-to-metal friction coefficient high and is excellent in anti-seizure properties, particularly suitable for belt type continuously variable transmissions.

The lubricating oil composition of the present invention is also excellent in performances required of transmission fluids other than those described above and thus is suitably used for the automatic or manual transmission and the differential gears, of automobiles, construction machines and agricultural machines. Moreover, the lubricating oil composition can be used as gear oils for industrial uses; lubricating oils for the gasoline engines, diesel engines or gas engines of automobiles such as two- and four-wheeled vehicles, power generators, and ships; turbine oils; and compressor oils.

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below.

The lubricating oil composition of the present invention comprises a lubricating base oil and at least a boron-containing ashless dispersant as Component (A), a metallic detergent as Component (B) and a friction modifier as Component (C) each in a specific amount.

No particular limitation is imposed on the lubricating base oil of the lubricating oil composition of the present invention (hereinafter simply referred to as “the lubricating oil composition”), which may be a mineral base oil or synthetic base oil that is usually used in lubricating oil.

Specific examples of the mineral base oil include those which can be produced by subjecting a lubricating oil fraction produced by vacuum-distilling an atmospheric distillation bottom oil resulting from atmospheric distillation of a crude oil, to any one or more treatments selected from solvent deasphalting, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, and hydrorefining; wax-isomerized mineral oils; and those produced by isomerizing GTL WAX (Gas to Liquid Wax).

The mineral based oil used in the present invention is preferably a hydrocracked mineral base oil. Alternatively, the mineral base oil is preferably a wax-isomerized isoparaffin base oil, which is produced by isomerizing a raw material oil containing 50 percent by mass or more of wax such as a petroleum-based wax or Fischer-Tropsch synthetic oil. Although these base oils may be used alone or in combination, the sole use of a wax-isomerized base oil is preferable.

Specific examples of the synthetic base oils include polybutenes and hydrogenated compounds thereof; poly-α-olefins such as 1-octene oligomer, 1-decene oligomer and 1-dodecene oligomer or hydrogenated compounds thereof; diesters such as ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate and di-2-ethylhexyl sebacate; polyol esters such as neopentylglycol ester, trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate and pentaerythritol pelargonate; aromatic synthetic oils such as alkylnaphthalenes, alkylbenzenes, and aromatic esters; and mixtures of the foregoing.

No particular limitation is imposed on the 100° C. kinematic viscosity of the lubricating base oil used in the present invention, which is, however, preferably 2 mm²/s or higher, more preferably 2.5 mm²/s or higher, particularly preferably 3 mm²/s or higher and preferably 8 mm²/s or lower, more preferably 6 mm²/s or lower, more preferably 4.5 mm²/s or lower, particularly preferably 4 mm²/s or lower. A base oil with a 100° C. kinematic viscosity of higher than 8 mm²/s is not preferable because the resulting lubricating oil composition would be poor in low temperature viscosity characteristics while a base oil with a 100° C. kinematic viscosity of lower than 2 mm²/s is not also preferable because the resulting lubricating oil composition would be poor in lubricity due to its insufficient oil film formation at lubricating sites and large in evaporation loss of the lubricating base oil.

The 100° C. kinematic viscosity used herein denotes the 100° C. kinematic viscosity determined in accordance with ASTM D-445.

No particular limitation is imposed on the 40° C. kinematic viscosity of the lubricating base oil used in the present invention, which is, however, preferably 8.0 mm²/s or higher, more preferably 8.5 mm²/s or higher, particularly preferably 9.0 mm²/s or higher and preferably 40 mm²/s or lower, more preferably 30 mm²/s or lower, more preferably 25 mm²/s or lower, particularly preferably 20 mm²/s or lower. A lubricating base oil with a 40° C. kinematic viscosity of higher than 40 mm²/s is not preferable because the resulting lubricating oil composition would be poor in low temperature viscosity characteristics whilst a lubricating base oil with a kinematic viscosity of lower than 8.0 mm²/s is not also preferable because the resulting lubricating oil composition would be poor in lubricity due to its insufficient oil film formation at lubricating sites and would be large in evaporation loss of the composition.

The 40° C. kinematic viscosity used herein denotes the 40° C. kinematic viscosity determined in accordance with ASTM D-445.

No particular limitation is imposed on the viscosity index of the lubricating base oil, which is, however, preferably 100 or greater, more preferably 120 or greater, more preferably 130 or greater, particularly preferably 140 or greater and usually 200 or less, preferably 160 or less. The use of a lubricating base oil having a viscosity index of greater than 100 renders it possible to produce a composition exhibiting excellent viscosity characteristics from low temperatures to high temperatures. Whilst, if the viscosity index is too high, the resulting composition would tend to be high in viscosity at low temperatures.

The lubricating base oil used in the present invention may be any one of the above-described mineral base oils and synthetic base oils or a mixture of two or more types selected therefrom. For example, the base oil may be one or more type of the mineral base oils, one or more type of the synthetic base oils or a mixed oil of one or more type of the mineral base oils and one or more type of the synthetic base oils.

In order to improve the low temperature viscosity characteristics and viscosity index of the lubricating oil composition, the lubricating base oil is preferably a low viscosity base oil having a 40° C. kinematic viscosity of 8 to 14 mm²/s, or a mix base oil comprising a combination of two or more types of base oils selected from low viscosity base oils having a 40° C. kinematic viscosity of 8 to 14 mm²/s and relatively high viscosity base oils. When this mix base oil is used, a base oil having a 40° C. kinematic viscosity of 8 to 14 mm²/s is preferably blended in an amount of at least 20 percent by mass or more, preferably 40 percent by mass or more.

The low viscosity base oil has a 40° C. kinematic viscosity of 8 to 14 mm²/s, preferably 9 to 12 mm²/s and a 100° C. kinematic viscosity of 2 mm²/s or higher and lower than 3.5 mm²/s.

Whilst, the relatively high viscosity base oil has a 40° C. kinematic viscosity of 15 to 25 mm²/s and a 100° C. kinematic viscosity of 3.5 mm²/s or higher and 4.5 mm²/s or lower.

The use of a mixture of the above-described low viscosity base oil and relatively high viscosity base oil can enhance the viscosity index.

The above-described low viscosity base oil has a viscosity index of preferably 110 or greater, more preferably 120 or greater, more preferably 125 or greater while the relatively high viscosity base oil has a viscosity index of preferably 125 or greater, more preferably 130 or greater, more preferably 135 or greater.

No particular limitation is imposed on the sulfur content of the lubricating base oil used in the present invention, which is, however, preferably 0.1 percent by mass or less, more preferably 0.01 percent by mass or less, more preferably 0.005 percent by mass or less, particularly preferably 0.001 percent by mass or less, most preferably substantially 0. A composition with excellent oxidation stability can be produced by reducing the sulfur content of the lubricating base oil.

The lubricating oil composition of the present invention contains a boron-containing ashless dispersant as Component (A).

Examples of the boron-containing ashless dispersant include boronated ashless dispersants produced by boronating an ashless dispersant.

Examples of the ashless dispersant include the following nitrogen compounds, which may be used alone or in combination:

(A1) succinimides having at least one straight-chain or branched alkyl or alkenyl group having 40 to 400 carbon atoms per molecule, or derivatives thereof;

(A2) benzylamines having at least one straight-chain or branched alkyl or alkenyl group having 40 to 400 carbon atoms per molecule, or derivatives thereof; and

(A3) polyamine having at least one straight-chain or branched alkyl or alkenyl group having 40 to 400 carbon atoms per molecule, or derivatives thereof.

The carbon number of the alkyl or alkenyl group of the ashless dispersant is preferably 40 to 400, more preferably 60 to 350. If the carbon number of the alkyl or alkenyl group is fewer than 40, the compound would tend to be degraded in solubility in the lubricating base oil. Whereas, if the carbon number of the alkyl or alkenyl group is more than 400, the resulting lubricating oil composition would be degraded in low-temperature fluidity.

The alkyl or alkenyl group may be straight-chain or branched but is preferably a branched alkyl or alkenyl group derived from oligomers of olefins such as propylene, 1-butene or isobutylene or a cooligomer of ethylene and propylene.

Specific examples of (A1) succinimides include compounds represented by formulas (1) and (2):

In formula (1), R¹ is an alkyl or alkenyl group having 40 to 400, preferably 60 to 350, and a is an integer of 1 to 5, preferably 2 to 4.

In formula (2), R² and R³ are each independently an alkyl or alkenyl group having 40 to 400, preferably 60 to 350, and b is an integer of 0 to 4, preferably 1 to 3.

Succinimides include mono-type succinimides wherein a succinic anhydride is added to one end of a polyamine, as represented by formula (1) and bis-type succinimides wherein a succinic anhydride is added to both ends of a polyamine, as represented by formula (2). The lubricating oil composition may contain either type of the succinimides or a mixture thereof.

No particular limitation is imposed on the method for producing the succinimides. For example, a method may be used, wherein an alkyl or alkenyl succinimide produced by reacting a compound having an alkyl or alkenyl group having 40 to 400 carbon atoms with maleic anhydride at a temperature of 100 to 200° C. is reacted with a polyamine. Examples of the polyamine include diethylene triamine, triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine.

Specific examples of (A2) benzylamines include compounds represented by formula (3):

In formula (3), R¹ is an alkyl or alkenyl group having 40 to 400, preferably 60 to 350 and r is an integer of 1 to 5, preferably 2 to 4.

No particular limitation is imposed on the method for producing the benzylamines. They may be produced by reacting a polyolefin such as a propylene oligomer, polybutene, or ethylene-α-olefin copolymer with a phenol so as to produce an alkylphenol and then subjecting the alkylphenol to Mannich reaction with formaldehyde and a polyamine such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, or pentaethylenehexamine.

Specific examples of (A3) polyamines include compounds represented by formula (4):

R¹—NH—(CH₂CH₂NH)_(k)—H  (4).

In formula (4), R¹ is an alkyl or alkenyl group having 40 to 400, preferably 60 to 350 and k is an integer of 1 to 5, preferably 2 to 4.

No particular limitation is imposed on the method for producing the polyamines. For example, the polyamines may be produced by chlorinating a polyolefin such as a propylene oligomer, polybutene, or ethylene-α-olefin copolymer and reacting the chlorinated polyolefin with ammonia or a polyamine such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

Boronation is generally carried out by allowing the above-described nitrogen-containing compound to react with boric acid to neutralize the whole or part of the remaining amino and/or imino groups.

Examples of a method of producing a boronated succinimide are those disclosed in Japanese Patent Publication Nos. 42-8013 and 42-8014 and Japanese Laid-Open Patent Publication Nos. 51-52381 and 51-130408. More specifically, a boronated succinimide may be produced by mixing polyamine and polyalkenylsuccinic acid (anhydride) with a boron compound such as boric acid, a boric acid ester, or a borate in a solvent including alcohols, organic solvent such as hexane or xylene, or a light fraction lubricating base oil and by heating the mixture under appropriate conditions.

In the present invention, if the boron-containing ashless dispersant contains boron in such an amount that is required of the lubricating oil composition in the present invention, it may be used in combination with a non-boronated ashless dispersant so as to enhance the stability of the composition.

However, the sole use of the boron-containing ashless dispersant is preferable in order to achieve the purposes of the present invention such as enhancement in anti-wear properties and anti-seizure properties.

In the present invention, the boron-containing ashless dispersant is preferably a boronated succinimide because of its stability as a compound.

The molecular weight of the hydrocarbon group of the boron-containing succinimide is preferably 500 or greater, more preferably 700 or greater, more preferably 900 or greater. The molecular weight is preferably 2000 or less, more preferably 1500 or less. If the molecular weight is less than 500, the resulting composition would be high in friction coefficient and thus less effective in fuel saving. Whilst, the molecular weight exceeds 2000, it would be substantially difficult to synthesize the boron-containing succinimide.

In the present invention, the boron content of the boron-containing ashless dispersant is preferably 1.0 percent by mass or more, more preferably 1.5 percent by mass or more. The boron content is also preferably 3 percent by mass or less, more preferably 2.5 percent by mass or less, particularly preferably 2.4 percent by mass or less.

If the boron content is less than 1.0 percent by mass, the resulting composition may not obtain anti-wear properties and anti-seizure properties that ate the purposes of the present invention. If the boron content exceeds 3 percent by mass, generation of precipitation may be concerned and may cause the resulting composition to be poor in stability.

In the present invention, the nitrogen content of the boron-containing ashless dispersant is preferably 1.0 percent by mass or more, more preferably 1.5 percent by mass or more. The nitrogen content is preferably 3 percent by mass or less, more preferably 2.5 percent by mass or less, particularly preferably 2.0 percent by mass or less.

If the nitrogen content is less than 1.0 percent by mass, the resulting composition may not achieve boronation that is a purpose of the present invention. If the nitrogen content exceeds 3 percent by mass, the resulting composition may cause rather deterioration of anti-wear properties.

In the present invention, the content of Component (A) is necessarily 300 ppm by mass or more, preferably 400 ppm by mass or more, more preferably 600 ppm by mass or more on a boron basis on the basis of the total lubricating oil composition mass. The upper limit is 1000 ppm by mass or less, preferably 900 ppm by mass or less, more preferably 850 ppm by mass or less, most preferably 800 ppm by mass or less. If the content of Component (A) is less than 300 ppm by mass, the resulting composition would be poor in extreme pressure properties. Whilst, the content exceeds 1000 ppm by mass, the resulting composition would exert harmful effects on friction materials and would be short in duration of anti-shudder properties. Generation of precipitation may be concerned and may cause the resulting composition to be poor in stability.

The lubricating oil composition of the present invention contains a metallic detergent with a total base number of 200 mgKOH/g or greater as Component (B).

The term “total base number” used herein denotes one measured by the perchloric acid potentiometric titration method in accordance with section 7 of JIS K2501 “Petroleum products and lubricants-Determination of neutralization number”.

Specific examples of the metallic detergent include alkaline earth metal sulfonates, alkaline earth metal phenates and alkaline earth metal salicylates. Any one or more metallic detergent selected from these compounds may be used. Particularly, calcium salts are preferable for the reason of friction characteristics.

Specific examples of the alkaline earth metal sulfonate include alkaline earth metal salts of alkyl aromatic sulfonic acids, produced by sulfonating an alkyl aromatic compound having a molecular weight of 100 to 1,500, preferably 200 to 700. Particularly, magnesium salts and/or calcium salts are preferably used. Calcium salts are particularly preferable for the reason of friction characteristics. Specific examples of the alkyl aromatic sulfonic acids include petroleum sulfonic acids and synthetic sulfonic acids.

Examples of the alkaline earth metal phenates include an alkali metal/alkaline earth metal salt of an alkylphenol having at least one straight-chain or branched alkyl group having 4 to 30, preferably 6 to 18 carbon atoms, an alkylphenolsulfide produced by reacting the alkylphenol with sulfur or a Mannich reaction product of an alkylphenol produced by reacting the alkylphenol with formaldehyde. Particularly, magnesium salts and/or calcium salts are preferable.

Specific examples of the alkaline earth metal salicylates include alkali metal/alkaline earth metal salts of alkyl salicylic acids having at least one straight chain or branched alkyl group having 4 to 30, preferably 6 to 18 carbon atoms. Particularly, magnesium salts and/or calcium salts are preferable.

The alkaline earth metal sulfonates, alkaline earth metal phenates, and alkaline earth metal salicylates if having a total base number of 200 mgKOH/g or greater include neutral salts (normal salts) produced by reacting alkyl aromatic sulfonic acids, alkylphenols, alkylphenolsulfides, Mannich reaction products of alkylphenols or alkylsalicylic acids directly with a metallic base such as an alkaline earth metal oxide or hydroxide or produced by converting alkyl aromatic sulfonic acids, alkylphenols, alkylphenolsulfides, Mannich reaction products of alkylphenols or alkylsalicylic acids to alkali metal salts such as sodium salts and potassium salts, followed by substitution with an alkaline earth metal salt; basic salts produced by heating these neutral salts (normal salts) with an excess amount of an alkaline earth metal salt or an alkaline earth metal base (alkaline earth metal hydroxide or oxide) in the presence of water; and overbased salts (ultrabasic salts) produced by reacting these neutral salts with a base such as an alkali metal or alkaline earth metal hydroxide in the presence of carbonic acid gas.

These reactions are generally carried out in a solvent (aliphatic hydrocarbon solvents such as hexane, aromatic hydrocarbon solvents such as xylene, and light lubricating base oil). Although metallic detergents are usually commercially available as diluted with a light lubricating base oil, it is preferable to use a metallic detergent whose metal content is from 1.0 to 20 percent by mass, preferably from 2.0 to 16 percent by mass.

The metallic detergent used in the present invention is preferably an overbased salt.

The content of Component (B) in the present invention is necessarily 100 ppm by mass or more, preferably 200 ppm by mass or more, more preferably 300 ppm by mass or more, more preferably 350 ppm by mass or more on a metal basis on the basis of the total lubricating oil composition mass. The content of Component (B) is also preferably 1200 ppm by mass or less, more preferably 1000 ppm by mass or less, more preferably 800 ppm by mass or less, particularly preferably 600 ppm by mass or less, most preferably 450 ppm by mass or less. If the content is less than 100 ppm by mass, the resulting composition would tend to be insufficient in friction characteristic enhancing effect. Whilst, if the content exceeds 1200 ppm by mass, the resulting composition would be degraded in friction characteristics due to harmful effects on friction materials of a wet clutch.

The metallic detergent used in the present invention is preferably calcium sulfonate. The sole use of calcium sulfonate is preferable. This is because the friction characteristics of calcium sulfonate are mostly conformed with friction characteristics sought by the present invention.

In the lubricating oil composition of the present invention, the content of Component (A) and the content of Component (B) are importantly within a specific range. That is, on the basis of the total lubricating oil composition mass, the ratio (Bo/M) of the content of Component (A) on a boron basis (Bo:ppm by mass) to the content of Component (B) on a metal basis (M:ppm by mass) is necessarily from 0.5 to 4. The lower limit Bo/M value is 0.5 or greater, preferably 0.6 or greater, more preferably 0.7 or greater, particularly preferably 1.0 or greater. The upper limit value is 4 or less, preferably 3.5 or less, preferably 3 or less, more preferably 2.5 or less, particularly preferably 2 or less. If the Bo/M is less than 0.5, the resulting composition would be insufficient in metal-to-metal friction coefficient enhancing effect. Whilst, the Bo/M exceeds 4, the resulting composition would also be insufficient in metal-to-metal friction coefficient enhancing effect.

The lubricating oil composition of the present invention also contains a friction modifier as Component (C).

The friction modifier may be any compound that has been generally used as a friction modifier in the field of lubricating oils. Specific examples include amine compounds, imide compounds, fatty acid esters, fatty acid amides, and fatty acid metal salts, each having per molecule at least one alkyl or alkenyl group having 6 to 30 carbon atoms, particularly a straight-chain alkyl or alkenyl group having 6 to 30 carbon atoms.

Examples of the amine compound include straight-chain or branched, preferably straight-chain aliphatic monoamines and aliphatic polyamines, each having 6 to 30 carbon atoms, and alkyleneoxide adducts of these aliphatic amines.

Examples of the imide compound include succinimides having a straight-chain or branched alkyl or alkenyl group having 6 to 30 carbon atoms and/or modified products thereof with a carboxylic acid, boric acid, phosphoric acid or sulfuric acid.

Examples of the fatty acid ester include esters of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms with aliphatic monohydric alcohols or aliphatic polyhydric alcohols. Examples of the fatty acid amides include amides of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms with aliphatic monoamines or aliphatic polyamines.

Examples of the fatty acid metal salts include alkaline earth metal salts (magnesium salts or calcium salts) or zinc salts of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms.

In the present invention, the lubricating oil composition contains preferably one or two types selected from amine-based friction modifiers, ester-based friction modifiers, amide-based friction modifiers, fatty acid-based friction modifiers and particularly preferably contains one or two types selected from amine-based friction modifiers, fatty acid-based friction modifiers and amide-based friction modifiers with the objective of further enhancing fatigue life. When the lubricating oil composition for a driving force transmission mechanism of the present invention is particularly used in an automatic transmission or a continuously variable transmission, an imide-based friction modifier is preferably contained with the objective of significantly enhancing the durability of anti-shudder properties.

The content of the friction modifier is 0.01 percent by mass or more, preferably 0.05 percent by mass or more, more preferably 0.1 percent by mass or more, most preferably 0.3 percent by mass or more on the basis of the total composition mass. The content is also 5 percent by mass or less, preferably 3 percent by mass or less, more preferably 1 percent by mass, more preferably 0.5 percent by mass or less. If the content is less than 0.01 percent by mass, it would be difficult to ensure the necessary anti-shudder properties. Whilst, if the content exceeds 5 percent by mass, it would be difficult to ensure the necessary metal-to-metal friction coefficient.

The lubricating oil composition of the present invention preferably further contains a phosphorus-containing additive as Component (D). Addition of Component (D) renders it possible to further enhance the anti-wear properties and anti-seizure properties and furthermore the friction characteristics of a wet clutch.

Examples of Component (D) that is a phosphorus-containing additive include zinc alkyldithiophosphates, phosphoric acid, phosphorous acid, phosphoric acid monoester, phosphoric acid diesters, phosphoric acid triesters, phosphorous acid monoesters, phosphorous acid diesters, phosphorous acid triesters, salts of phosphoric acid (phosphorous acid), and mixtures thereof.

Among these Compounds (D), those other than phosphoric acid and phosphorous acid are compounds containing a hydrocarbon group having usually 2 to 30, preferably 3 to 20 carbon atoms. Specific examples of the hydrocarbon group having 2 to 30 carbon atoms include alkyl, cycloalkyl, alkyl-substituted cycloalkyl, alkenyl, aryl, alkyl-substituted aryl, and aryl-substituted alkyl groups. These alkyl groups may be straight-chain or branched.

Specific examples of salts of phosphoric acid (phosphorous acid) include those produced by allowing phosphoric acid monoester, phosphoric acid diester, phosphorous acid monoester or phosphorous acid diester to react with a nitrogen-containing compound such as ammonia or an amine compound having in its molecules only a hydrocarbon group or hydroxyl-containing hydrocarbon group having 1 to 8 carbon atoms so as to neutralize the whole or part of the remaining acid hydrogen.

Any one or more of these Components (D) may be blended.

In the present invention, alkyl or alkenyl phosphorous acid esters are preferably used. Alkyl phosphorous acid esters having 8 or fewer carbon atom, preferably 5 or fewer carbon atoms are particularly preferably used.

In the present invention, phosphorous acid and an alkyl or alkenyl phosphorous acid ester are preferably used in combination.

When phosphorous acid and an alkyl or alkenyl phosphorous acid ester are used in combination, the phosphorus amount ratio of phosphorous acid:the alkyl or alkenyl phosphorous acid ester is preferably 1:0.2 to 1:3.5, more preferably 1:0.5 to 1:3, more preferably 1:1 to 1:2. If the ratio of phosphorous acid is less than 0.2 or exceeds 10, the balance of the metal-to-metal friction coefficient and anti-shudder properties would be degraded.

When the lubricating oil composition of the present invention is blended with Component (D), no particular limitation is imposed on the amount thereof, which is, however, preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, more preferably 200 ppm by mass or more, most preferably 400 ppm by mass or more and preferably 2000 ppm by mass or less, more preferably 1500 ppm by mass or less, more preferably 1000 ppm by mass or less, particularly preferably 800 ppm by mass or less, most preferably 600 ppm by mass or less on a phosphorus basis on the basis of the total lubricating oil composition mass with the objective of enhancing the friction coefficient of a wet clutch and obtaining excellent oxidation stability for the lubricating oil composition.

If the amount on a phosphorous basis is less than 50 ppm by mass, the resulting composition would not be sufficient in anti-wear properties or metal-to-metal friction coefficient and also be insufficient in anti-shudder properties. If the amount exceeds 2000 ppm by mass, Component (D) would exert harmful effect on the oxidation stability or sealing materials.

The lubricating oil composition of the present invention may contain Component (D) that is a phosphorus-containing additive and an extreme pressure additive other than Component (D) in combination. Such extreme pressure additive that may be used in combination may be any compounds that are generally used as extreme pressure additives for lubricating oil. Examples of the extreme pressure additive include sulfur-containing compounds such as disulfides, sulfurized olefins, and sulfurized fats and oils. Any one or more types of compounds selected from these compounds may be blended in any amount. The amount of the extreme pressure additive is usually from 0.01 to 5.0 percent by mass on the basis of the total lubricating oil composition mass.

The lubricating oil composition of the present invention preferably contains a viscosity index improver as Component (E). Specific examples of the viscosity index improver include non-dispersant type viscosity index improvers such as polymers or copolymers of one or more monomers selected from various methacrylic acid esters or hydrogenated compounds thereof and dispersant type viscosity index improvers such as copolymers of various methacrylic acid esters further containing nitrogen compounds.

Specific examples of other viscosity index improver include non-dispersant type or dispersant type ethylene-α-olefin copolymers (of which α-olefin may be propylene, 1-butene or 1-pentene) or hydrogenated compounds thereof; polyisobutylenes or hydrogenated compounds thereof; hydrogenated compounds of styrene-diene copolymers; styrene-maleic anhydride ester copolymers; and polyalkylstyrenes.

The molecular weight of the viscosity index improver is selected considering the shear stability. Specifically, the number-average molecular weight of the non-dispersant or dispersant type polymethacrylate is from 5,000 to 150,000, preferably from 5,000 to 35,000. The number-average molecular weight of polyisobutylenes or hydrogenated compounds thereof is from 800 to 5,000, preferably from 1,000 to 4,000. The number-average molecular weight of ethylene-α-olefin copolymers or hydrogenated compounds thereof is from 800 to 150,000, preferably from 3,000 to 12,000. Among these viscosity index improvers, the use of ethylene-α-olefin copolymers or hydrogenated compounds thereof renders it possible to produce a lubricating oil composition which is particularly excellent in shear stability. One or more compounds selected from these viscosity index improvers may be blended in any amount in the lubricating oil composition of the present invention. The content of the viscosity index improver is usually from 0.1 to 40.0 percent by mass, on the basis of the total amount of the composition.

The viscosity index improver used in the present invention is preferably a polymer or copolymer of a methacrylic acid ester that is polymethacrylate. This is because polymethacrylate has enhanced low temperature viscosity characteristics and viscosity index enhancing effect as a viscosity index improver.

The viscosity index improver has a weight-average molecular weight of preferably 5,000 to 100,000, more preferably 10,000 or greater and more preferably 70,000 or less. It is preferred to use a viscosity index improver having a weight-average molecular weight of 5,000 or greater and less than 30,000 in combination with a viscosity index improver having a weight-average molecular weight of 30,000 or greater and 70,000 or less. The viscosity index improver having a weight-average molecular weight of 30,000 or greater and 70,000 or less has preferably a weight-average molecular weight of 60,000 or less.

When those each having a weight-average molecular weight of 5,000 or greater and less than 30,000 and a weight-average molecular weight of 30,000 or greater and 70,000 or less, the mass ratio as additives of that having a weight-average molecular weight of 5,000 or greater and less than 30,000:that having a weight-average molecular weight of 30,000 or greater and less than 70,000 is preferably 1:0.02 to 1:1, more preferably 1:0.05 to 1:0.8, more preferably 1:0.1 to 1:0.5.

The reason to use two types of polymethacrylates in combination is that shear stability, and low temperature viscosity characteristics and viscosity index enhancing effect are best-balanced in the present invention.

If necessary, the lubricating oil composition of the present invention may be blended with one or more of various additives other than the above-described additives, such as antioxidants, corrosion inhibitors, rust inhibitors, demulsifiers, metal deactivators, pour point depressants, rubber swelling agents, antifoamers and colorants for the purposes of further enhancing the properties of the composition.

The antioxidant may be any antioxidant that has been usually used in lubricating oil, such as phenol- or amine-based compounds. Specific examples of the antioxidant include alkylphenols such as 2-6-di-tert-butyl-4-methylphenol; bisphenols such as methylene-4,4-bisphenol (2,6-di-tert-butyl-4-methylphenol); naphthylamines such as phenyl-α-naphthylamine; dialkyldiphenylamines; zinc dialkyldithiophosphates such as zinc di-2-ethylhexyldithiophosphate; and esters of (3,5-di-tert-butyl-4-hydroxyphenyl) fatty acid (such as propionic acid) with a monohydric or polyhydric alcohol such as methanol, octadecanol, 1,6-hexanediol, neopentyl glycol, thiodiethylene glycol, triethylene glycol and pentaerythritol. Any one or more type selected from these antioxidants may be used in any amount. In the present invention, an amine-based compound and a phenol-based compound are preferably used in combination.

Examples of the corrosion inhibitor include benzotriazole-, tolyltriazole-, thiadiazole-, and imidazole-types compounds.

Examples of the rust inhibitor include petroleum sulfonates, alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenyl succinic acid esters, and polyhydric alcohol esters.

Examples of the demulsifier include polyalkylene glycol-based non-ionic surfactants such as polyoxyethylenealkyl ethers, polyoxyethylenealkylphenyl ethers, and polyoxyethylenealkylnaphthyl ethers.

Examples of the metal deactivator include imidazolines, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles and derivatives thereof, 1,3,4-thiadiazolepolysulfide, 1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamate, 2-(alkyldithio)benzoimidazole, and β-(o-carboxybenzylthio)propionitrile.

The pour point depressants may be selected from any conventional pour point depressants depending on the lubricating base oil. The pour point depressants is preferably a poly(meth)acrylate-based pour point depressant having a weight-average molecular weight of 50,000 to 300,000, preferably 60,000 to 300,000, particularly preferably 100,000 to 250,000.

The antifoamer may be any compounds that have been usually used as anti-foaming agents for lubricating oil. Examples of such compounds include silicones such as dimethylsilicone and fluorosilicone. Any one or more of compounds selected from these compounds may be contained in any amount.

The colorant may be any compound that has been usually used and may be blended in any amount. The amount is usually from 0.001 to 1.0 percent by mass on the total composition mass basis.

When these additives are contained in the lubricating oil composition of the present invention, the antioxidant, corrosion inhibitor, rust inhibitor and demulsifier are each contained in an amount of 0.005 to 5 percent by mass, the metal deactivator is contained in an amount of 0.005 to 1 percent by mass, the pour point depressant is contained in an amount of 0.05 to 1 percent by mass, the antifoamer is contained in an amount of 0.0005 to 1 percent by mass, and the colorant is contained in an amount of 0.001 to 1 percent by mass, all on the total composition mass basis.

The lubricating oil composition of the present invention has a 100° C. kinematic viscosity of preferably 4 mm²/s or higher, more preferably 4.5 mm²/s or higher, more preferably 5 mm²/s or higher, particularly preferably 5.5 mm²/s or higher, most preferably 6 mm²/s or higher and preferably 9 mm²/s or lower, more preferably 8 mm²/s or lower, more preferably 7.5 mm²/s or lower, particularly preferably 7 mm²/s or lower, most preferably 6.5 mm²/s or lower.

If the kinematic viscosity is lower than 4 mm²/s, the resulting composition would fail to form oil film in a sufficient thickness and thus be insufficient in anti-wear properties. If the kinematic viscosity exceeds 9 mm²/s, the resulting composition would not only fail to provide sufficient fuel saving effect but also cause the startability at low temperatures to be insufficient.

The lubricating oil composition of the present invention has a 40° C. kinematic viscosity of preferably 10 mm²/s or higher, more preferably 12 mm²/s or higher, more preferably 15 mm²/s or higher and preferably 30 mm²/s or lower, more preferably 25 mm²/s or lower, more preferably 20 mm²/s or lower.

If the kinematic viscosity is lower than 10 mm²/s, the resulting composition would fail to form oil film in a sufficient thickness and thus be insufficient in anti-wear properties. If the kinematic viscosity exceeds 30 mm²/s, the resulting composition would be significantly poor in fuel saving properties.

The lubricating oil composition of the present invention has a −40° C. BF viscosity of preferably 20,000 mPa·s or lower, more preferably 15,000 mPa·s or lower, more preferably 10,000 mPa·s or lower, particularly preferably 8,000 mPa·s or lower, most preferably 7,000 mPa·s or lower. If the BF viscosity exceeds 20,000 mPa·s, it would tend to cause startability at low temperatures to be insufficient.

The lubricating oil composition of the present invention has a viscosity index of preferably 160 or greater, more preferably 180 or greater, more preferably 200 or greater, most preferably 210 or greater and preferably 300 or less, more preferably 250 or less, more preferably 230 or less. If the viscosity index is less than 160, the resulting composition would tend to be insufficient in fuel saving properties. A composition having a viscosity index of greater than 300 contains too much poly(meth)acrylate-based viscosity index improver and would tend to be insufficient in shear stability.

The lubricating oil composition for automatic transmissions of the present invention is suitably used for a continuously variable transmission having a metal belt. In particular, the lubricating oil composition is suitable for a continuously variable transmission having a chain belt type metal belt.

EXAMPLES

Hereinafter, the present invention will be described in more detail by way of the following examples and comparative examples, which should not be construed as limiting the scope of the invention.

Examples 1 to 18 and Comparative Examples 1 to 7

Lubricating oil compositions of Examples 1 to 18 and Comparative Examples 1 to 7 set forth in Table 1 were prepared and subjected to the following tests, the evaluation results of which are also set forth in Table 1. In Table 1, the ratio of the base oils is based on the total mass of the base oils, and the amount of each additive is on the basis of the total mass of the composition.

(1) Last non-seizure load (LNSL) evaluated by Four-Ball Extreme Pressure Test Method in accordance with ASTM D2783

(2) Wear scar diameter evaluated by Four-Ball Extreme Pressure Test Method in accordance with ASTM D4172

(3) Seizure load evaluated by Falex Seizure test in accordance with ASTM D 3233

(4) Metal-to-metal friction coefficient evaluated by LFW-1 Test in accordance with JASO Method (High Load Method) M358:2005

(5) Shudder durability test evaluated by LVFA durability test in accordance with JASO Method M349:2010

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Exemple 6 Example 7 Example 8 Base oil A-1a (base all total mass basis) mass % 65 65 65 65 65 65 65 65 Base oil A-1b (base oil total mass basis) mass % 35 35 35 35 35 35 35 35 Base oil A-2a (base oil total mass basis) mass % — — — — — — — — Base oil A-2b (base oil total mass basis) mass % — — — — — — — — Base oil kinematic viscosity  (40° C.) mm²/s 12.8 12.8 12.8 12.8 12.8 12.8 12.8 12.8 Base oil kinematic viscosity (100° C.) mm²/s 3.36 3.36 3.36 3.36 3.36 3.36 3.36 3.36 VI 140 140 140 140 140 140 140 140 Additive composition (total composition mass basis) Viscosity index improver B-1a mass % 10 10 10 10 10 10 10 10 Viscosity index improver B-1b mass % 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Boron-containing succinimide C-1a 3.5 3.5 3.5 3.5 1.75 3 3.5 3.5 Boron-containing succinimide C-1b Succinimide C-2 1.50 Phosphorus additive D-1 0.20 0.20 0.20 0.20 0.20 0.20 0.20 Phosphorus additive D-2 0.23 Phosphorus additive D-3 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 Ca sulfonate E-1 0.22 0.16 0.60 0.10 0.19 0.11 0.22 Ca sulfonate E-2 0.33 Ca sulfonate E-3 Friction Modifier F-1 Friction Modifier F-2 Friction Modifier F-3 1.50 1.50 1.50 1.50 1.50 1.50 1.50 0.15 Sulfur additive G-1 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 Antioxidant H-1 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 Content in composition Boron basis (Bo) mass ppm % 700 700 700 700 350 600 700 700 Calcium basis (M) mass ppm % 400 300 1100 180 350 210 400 400 Nitrogen content (N) mass ppm % 1505 1505 1505 1505 1155 1405 1505 1505 Boron/calcium (B/Ca) ratio 1.8 2.3 0.6 3.9 1.0 2.9 1.8 1.8 Kinematic viscosity  (40° C.) mm²/s 25.5 25.5 25.5 25.5 25.5 25.5 25.5 25.5 (100° C.) mm²/s 6.26 6.26 6.26 6.26 6.26 6.26 6.26 6.26 VI 212 212 212 212 212 212 212 212 Four half extreme LNSL N 785 785 785 785 618 785 618 618 pressure Wear scar diameter mm 0.39 0.36 0.36 0.35 0.46 0.40 0.41 0.40 Falex seizure test lb 1360 1280 1380 1310 1120 1240 1330 1280 LFW-1 test (friction coefficient) 0.1 m/s 0.142 0.137 0.147 0.131 0.133 0.135 0.138 0.140 LVFA durability hr >240 >240 >240 >240 >240 >240 >240 >240 Example 9 Example 10 Example 11 Example 13 Example 14 Example 15 Base oil A-1a (base all total mass basis) mass % 65 65 65 0 20 50 Base oil A-1b (base oil total mass basis) mass % 35 35 35 100 80 50 Base oil A-2a (base oil total mass basis) mass % — — — — — — Base oil A-2b (base oil total mass basis) mass % — — — — — — Base oil kinematic viscosity  (40° C.) mm²/s 12.8 12.8 12.8 9.07 10.0 11.8 Base oil kinematic viscosity (100° C.) mm²/s 3.36 3.36 3.36 2.62 2.82 3.16 VI 140 140 140 127 131 137 Additive composition (total composition mass basis) Viscosity index improver B-1a mass % 10 10 10 10 10 10 Viscosity index improver B-1b mass % 3.5 3.5 35 35 3.5 3.5 Boron-containing succinimide C-1a 3.5 3.5 3.5 3.5 3.5 3.5 Boron-containing succinimide C-1b Succinimide C-2 Phosphorus additive D-1 0.20 0.20 0.33 0.20 0.20 0.20 Phosphorus additive D-2 Phosphorus additive D-3 0.07 0.07 0.07 0.07 0.07 Ca sulfonate E-1 0.22 0.22 0.22 0.22 022 0.22 Ca sulfonate E-2 Ca sulfonate E-3 Friction Modifier F-1 0.20 Friction Modifier F-2 0.10 Friction Modifier F-3 0.80 0.80 0.15 1.50 1.50 1.50 Sulfur additive G-1 0.10 0.10 0.10 0.10 0.10 0.10 Antioxidant H-1 0.50 0.50 0.50 0.50 0.50 0.50 Content in composition Boron basis (Bo) mass ppm % 700 700 700 700 700 700 Calcium basis (M) mass ppm % 400 400 400 400 400 400 Nitrogen content (N) mass ppm % 1505 1605 1505 1505 1505 1505 Boron/calcium (B/Ca) ratio 1.6 1.8 1.8 1.8 1.8 1.8 Kinematic viscosity  (40° C.) mm²/s 25.5 25.5 25.5 23.4 24.3 25.5 (100° C.) mm²/s 6.26 6.26 6.26 5.52 5.72 6.06 VI 212 212 212 188 191 198 Four half extreme LNSL N 618 618 618 618 618 618 pressure Wear scar diameter mm 0.44 0.41 0.32 0.44 0.42 0.41 Falex seizure test lb 1180 1210 1360 1140 1180 1280 LFW-1 test (friction coefficient) 0.1 m/s 0.132 0.131 0.143 0.144 0.144 0.142 LVFA durability hr >240 >240 >240 >240 >240 >240 Example 16 Example 17 Example 18 Comparative Comparative Comparative Base oil A-1a (base all total mass basis) mass % 80 65 65 65 Base oil A-1b (base oil total mass basis) mass % 20 35 35 35 Base oil A-2a (base oil total mass basis) mass % — 80 50 — — — Base oil A-2b (base oil total mass basis) mass % — 20 50 — — — Base oil kinematic viscosity  (40° C.) mm²/s 13.9 18.1 15.6 12.79 12.79 12.79 Base oil kinematic viscosity (100° C.) mm²/s 3.57 3.99 3.60 3.356 3.356 3.356 VI 144 118 113 140 140 140 Additive composition (total composition mass basis) Viscosity index improver B-1a mass % 10 10 10 10 10 10 Viscosity index improver B-1b mass % 3.5 2 2 3.5 3.5 3.5 Boron-containing succinimide C-1a 3.5 3.5 3.5 3.5 1.75 3.5 Boron-containing succinimide C-1b Succinimide C-2 1.50 Phosphorus additive D-1 0.20 0.20 0.20 0.20 0.20 0.20 Phosphorus additive D-2 Phosphorus additive D-3 0.07 0.07 0.07 0.07 0.07 0.07 Ca sulfonate E-1 0.22 0.22 0.22 0.05 0.54 Ca sulfonate E-2 Ca sulfonate E-3 1.01 Friction Modifier F-1 Friction Modifier F-2 Friction Modifier F-3 1.50 1.50 1.50 0.15 0.15 0.15 Sulfur additive G-1 0.10 0.10 0.10 0.10 0.10 0.10 Antioxidant H-1 0.50 0.50 0.50 0.50 0.50 0.50 Content in composition Boron basis (Bo) mass ppm % 700 700 700 700 350 700 Calcium basis (M) mass ppm % 400 400 400 100 1000 400 Nitrogen content (N) mass ppm % 1505 1150 1160 1505 1155 1505 Boron/calcium (B/Ca) ratio 1.8 1.8 1.8 7.0 0.4 1.8 Kinematic viscosity  (40° C.) mm²/s 26.3 29.5 27.6 25.5 25.5 25.5 (100° C.) mm²/s 6.47 6.48 6.09 6.26 6.26 6.26 VI 215 183 178 212 212 212 Four half extreme LNSL N 785 785 785 785 618 618 pressure Wear scar diameter mm 0.32 0.35 0.40 0.43 0.51 0.55 Falex seizure test lb 1360 1310 1280 1310 990 960 LFW-1 test (friction coefficient) 0.1 m/s 0.142 0.136 0.137 0.115 0.128 0.111 LVFA durability hr >240 >240 >240 >240 216 168 Comparative Comparative Comparative Comparative Base oil A-1a (base all total mass basis) mass % 65 65 65 65 Base oil A-1b (base oil total mass basis) mass % 35 35 35 35 Base oil A-2a (base oil total mass basis) mass % — — — — Base oil A-2b (base oil total mass basis) mass % — — — — Base oil kinematic viscosity  (40° C.) mm²/s 12.79 12.79 12.79 12.79 Base oil kinematic viscosity (100° C.) mm²/s 3.356 3.356 3.356 3.356 VI 140 140 140 140 Additive composition (total composition mass basis) Viscosity index improver B-1a mass % 10 10 10 10 Viscosity index improver B-1b mass % 3.5 3.5 3.5 3.5 Boron-containing succinimide C-1a 2 6 3.5 Boron-containing succinimide C-1b 4.10 Succinimide C-2 1.00 Phosphorus additive D-1 0.20 0.20 0.20 0.20 Phosphorus additive D-2 Phosphorus additive D-3 0.07 0.07 0.07 0.07 Ca sulfonate E-1 0.11 0.11 0.54 0.08 Ca sulfonate E-2 Ca sulfonate E-3 Friction Modifier F-1 Friction Modifier F-2 Friction Modifier F-3 0.15 0.15 0.15 0.15 Sulfur additive G-1 0.10 0.10 0.10 0.10 Antioxidant H-1 0.50 0.50 0.50 0.50 Content in composition Boron basis (Bo) mass ppm % 200 200 1200 700 Calcium basis (M) mass ppm % 200 200 1000 140 Nitrogen content (N) mass ppm % 1707 1205 2005 1505 Boron/calcium (B/Ca) ratio 1.0 1.0 1.2 5.0 Kinematic viscosity  (40° C.) mm²/s 25.5 25.5 25.5 25.5 (100° C.) mm²/s 6.26 6.26 6.26 6.26 VI 212 212 212 212 Four half extreme LNSL N 618 618 785 785 pressure Wear scar diameter mm 0.53 0.50 0.34 0.41 Falex seizure test lb 870 910 880 1280 LFW-1 test (friction coefficient) 0.1 m/s 0.118 0.116 0.129 0.121 LVFA durability hr >240 >240 120 >240 Base oil: hydrorefined mineral oil A-1a 40° C.: 15.65 mm²/s, 100° C.: 3.883 mm²/s, VI: 148, and synthetic oil sulfur content: <10 ppm, % C_(P): 92.5, % C_(H): 7.5, % C_(A): 0 A-1b 40° C.: 9.072 mm²/s, 100° C.: 2.621 mm²/s, VI: 127, sulfur content: <10 ppm, % C_(P): 91.8, C_(H): 8.2, % C_(A: 0) A-2a 40° C.: 20.01 mm²/s, 100° C.: 4.282 mm²/s, VI: 121, sulfur content: <10 ppm, % C_(P): 80.7, % C_(H): 19.3, % C_(A): 0 A-2b 40° C.: 12.38 mm²/s, 100° C.: 3.069 mm²/s, VI: 105, sulfur content: <10 ppm Viscosity index improver: B-1a polymethacrylate weight-average molecular weight (Mw): 20000 polymethacrylate B-1b polymethacrylate weight-average molecular weight (Mw): 50000 Boron-containing C-1a boronated succinimide: boron content (2.0 mass %), nitrogen content (2.3 mass %), succinimide weight molecular weight of hydrocarbon group: 1000 C-1b boronated succinimide: boron content (0.5 mass %), nitrogen content (2.0 mass %), weight molecular weight of hydrocarbon group: 2000 Succinimide C-2 non-boronated succinimide: nitrogen content (2.2 mass %) Phosphorus additive D-1 dibutylphosphite, P content (15.5%) D-2 diphenylhydrogen phosphite, P content (13.2%) D-3 phosphorus acid: P content (30.0 mass %) Ca sulfonate E-1 calcium sultanate: 500 BN, Ca content (18.4 mass %) E-2 calcium sultanate: 300 BN, Ca content (12.0 mass %) E-3 calcium sultanate: 70 BN, Ca content (4.0 mass %) Friction modifier F-1 carboxylic acid F-2 oleylamine F-3 amide Sulfur additive G-1 Sulfur content: 36.0% (1,3,4-thiadiazole compound) Antioxidant H-1 α-phenylnaphthylamine Four ball extreme pressure test ASTM D 2783 1800 rpm, LNSL Wear scar diameter: 392N, 1200 rpm, ASTM D 4172 80° C., 30 min Falex seizure test: 290 rpm, 110° C. ASTM D 3233 LFW-1test: JASO method (high load JASO M358:2005 method) LVFA durability test JASO method JASO M349:2010

As apparent from the results set forth in Table 1, the compositions of Comparative Examples 1 and 7 wherein the boron/metal (Bo/M) ratios are 7.0 and 5.0, respectively are lower in metal-to-metal friction coefficient evaluated by LFW-1 than those of Examples.

The composition of Comparative Example 2 wherein the boron/metal (Bo/M) ratio is 0.4 is lower in metal-to-metal friction coefficient evaluated by LFW-1 than those of Examples.

The composition of Comparative Example 3 wherein calcium sulfonate having a base number of 70 mgKOH/g was used is lower in metal-to-metal friction coefficient evaluated by LFW-1 than those of Examples and insufficient in anti-wear properties and anti-seizure properties.

The compositions of Comparative Examples 4 and 5 wherein an ashless dispersant containing boron was used but the amount thereof was 200 ppm by mass, and Comparative Example 6 wherein the amount of boron was 1200 ppm by mass are lower in metal-to-metal friction coefficient evaluated by LFW-1 than those of Examples and insufficient in anti-wear properties and anti-seizure properties. Furthermore, the composition of these comparative examples are also lower in metal-to-metal friction coefficient evaluated by LFW-1 giving harmful effect on the torque capacity. 

1. A lubricating oil composition for automatic transmissions comprising a base oil, and on the basis of the total mass of the composition: (A) a boron-containing ashless dispersant in an amount of 300 to 1000 ppm by mass on a boron basis; (B) a metallic detergent with a total base number of 200 mgKOH/g or greater in an amount of 100 to 1200 ppm by mass on a metal basis; and (C) a friction modifier in an amount of 0.01 to 5 percent by mass, the ratio (Bo/M) of the content of Component (A) on a boron basis (Bo:ppm by mass) to the content of Component (B) on a metal basis (M:ppm by mass) being from 0.5 to
 4. 2. The lubricating oil composition for automatic transmissions according to claim 1 wherein the lubricating base oil comprises one type of base oil or a mixture of two or more types of base oils, at least one type of base oil is a mineral base oil or synthetic base oil having a 40° C. kinematic viscosity of 8 to 14 mm²/s, the base oil is blended in an amount of 20 percent by mass or more, and the composition has a 40° C. kinematic viscosity of 10 to 30 mm²/s and a viscosity index of 160 or greater.
 3. The lubricating oil composition for automatic transmissions according to claim 1 further comprising (D) a phosphorus-containing additive in an amount of 50 to 2000 ppm by mass on a phosphorus basis on the basis of the total mass of the composition and (E) a viscosity index improver in an amount of 0.1 to 40 percent by mass on the basis of the total mass of the composition.
 4. The lubricating oil composition for automatic transmissions according to claim 1 wherein (A) the boron-containing ashless dispersant contains one percent by mass more of boron and 3 percent by mass or more of nitrogen.
 5. The lubricating oil composition for automatic transmissions according to claim 1 wherein (B) the metallic detergent consists of calcium sulfonate.
 6. The lubricating oil composition for automatic transmissions according to claim 1 wherein the composition is used for a continuously variable transmission with a metal belt. 